A microelectromechanical system by applicant is known e.g. from WO 2009/003958.
An electromechanical microswitch as described in U.S. Pat. No. 6,529,093 can be used for switching a radio frequency signal, in particular in GHz range. In particular for microelectronic circuits which are timed with very high frequencies in the GHz range, it is very helpful to have electromechanical microswitches which facilitate switching electrical connections on and off in a controlled manner. In U.S. Pat. No. 6,529,093 recited supra, a micromechanical switch is described which is made from a cantilever made from polysilicon and which is driven by an electrode arrangement to which an electrical potential is applied. Besides the electrode arrangement for driving the cantilever, a second electrode arrangement is provided therein for switching the RF signal. At least one of the electrodes of an electrode pair is thus provided with a dielectrical layer. The cantilever can thus also be configured as a bridge that is clamped on both sides. The layer configuration required for implementing the microswitch thus includes partially applied layers made from a dielectric material, conductors and polysilicon. Also in U.S. Pat. No. 6,639,488 a microswitch is described whose layer configuration is characterized by applying various dielectric and electrically conductive layers. Though in both documents production methods are used which are designated as CMOS compatible, they require method steps for producing the microswitches which are not required for producing microelectronic circuits.
In particular in circuits which are produced through the CMOS technology that is typically used in the semiconductor industry and which circuits are being used in wireless data transmissions and communications, typically electromechanical switches are being used which cannot be integrated together with electronic circuits on one chip. It would be much more cost-effective and advantageous in order to achieve further miniaturization to provide an electromechanical microswitch which is furthermore provided in a CMOS compatible manner so that an electromechanical microswitch can simultaneously be produced with the microelectronic circuit.
In view of this fact, it is important to generally understand the CMOS production process which is divided into a front-end of line (FEoL) portion and a back-end of line (BEoL) portion. While the process steps of the FEoL portion relate to producing the transistors directly on the surface of the silicon substrate, the transistors are connected with one another through electrical conductors in the BEoL portion. In particular, such connections are produced from the structuring of horizontal metal planes and vertical conductors (so-called Vias) which are embedded into electrically insulating layers between the horizontal metal planes. Thus, the processes performed in the two portions FEoL and BEoL differ substantially with respect to their thermal budget, in particular with respect to the level and duration of the process temperatures used. Thus, very high process temperatures occur in the FEoL portion, which are not reached again in the BEoL portion in order not to destroy the complex transistor build ups through the inter-diffusion processes.
As described supra, the recited solutions implement an electromechanical microswitch based on silicon, wherein the microswitch has to be produced through FEoL processes. From a process technology point of view, producing an electromechanical microswitch in the BEoL portion is much more advantageous.
U.S. Pat. No. 6,667,245 describes a method for producing a MEMS-RF switch in which Vias are being used as structural elements of a switch in the BEoL process.